A 3D image display apparatus making use of a hologram is configured to generate a reproduced light component from a hologram under illumination with an illumination light component and to display a 3D image from the reproduced light component thus generated. Another 3D image display apparatus is configured to make illumination light components of multiple wavelengths (e.g., three-color components of red, green, and blue) incident to a hologram, thereby enabling color display of a 3D image.
A first conventional technology known heretofore is a technology of making use of a photographic plate permitting high-resolution recording. In this first conventional technology, hologram recording is carried out by making reference light components and object light components of respective wavelengths incident to a photographic plate and thereby multiply recording holograms associated with the respective wavelengths on the photographic plate. On the other hand, reproduction is implemented by making illumination light components of the same wavelengths as those in the recording, incident from an identical incident direction to the holograms to generate reproduced light components of the wavelengths. This results in superimposing images of these reproduced light components on each other at the same position, thereby obtaining a color 3D image.
However, since in this first conventional technology the holograms associated with the respective wavelengths are multiply recorded on the photographic plate, the illumination light component of a wavelength λa is incident to the hologram associated with the wavelength λa to generate the reproduced light component of the wavelength λa, and the illumination light component of another wavelength λb (λa≠λb) is also incident to the hologram associated with the wavelength λa to generate a reproduced light component of the wavelength λb from the hologram associated with the wavelength λa as well. Among these reproduced light component of wavelength λa and reproduced light component of wavelength λb, the reproduced light component of wavelength λa is the light component necessary for color display of the original 3D image. In contrast to it, the reproduced light component of wavelength λb is a light component reproduced at a different position and at a different magnification from those of the original 3D image, and is thus a crosstalk component against the original 3D image to hider display of the 3D image. In order to avoid such crosstalk, therefore, recording is carried out by making the reference light components of multiple wavelengths incident from mutually different directions to the photographic plate where the object light components are incident approximately normally to the photographic plate, whereby crosstalk light components are prevented from being superimposed on the original 3D image in the reproduction.
As a second conventional technology, Kunihiko Takano et al. “Study of color holography 3D television with white light,” Proceedings of 3D Image Conference 2000, pp179–182 discloses a technology of making use of three types of spatial light modulators capable of presenting a hologram. Specifically, a first spatial light modulator presents a hologram associated with red light, a second spatial light modulator a hologram associated with green light, and a third spatial light modulator a hologram associated with blue light. Then a red illumination light component is made incident to the first spatial light modulator, a green illumination light component to the second spatial light modulator, and a blue illumination light component to the third spatial light modulator, whereby reproduced light components generated from the respective spatial light modulators are spatially superimposed, and zero-order transmitted light is removed by a mask disposed in a subsequent stage, thereby obtaining a color 3D image.
Furthermore, a third conventional technology is the technology described in Japanese Patent Application Laid-Open No. 2000-250387, which positively makes use of the pixel structure of the spatial light modulator being discrete. Specifically, when parallel light is made incident into an ordinary diffraction grating, there appear not only a zero-order diffracted wave but also first and higher-order diffracted waves. Likewise, reproduced light components generated from a spatial light modulator having the discrete pixel structure also include a zero-order diffracted wave and higher-order diffracted waves. Concerning two adjacent pixels in a spatial light modulator, where a presentation range is limited to a range in which phase differences between synthetic wavefronts of an object light component and a reference light component are less than n (i.e., a range without alias components) and where a hologram is presented on the spatial light modulator, wavefronts of higher-order diffracted waves of reproduced light components generated from the spatial light modulator upon incidence of the illumination light component coincide with those of the zero-order diffracted waves. However, directions of emergence from the spatial light modulator are different among orders. The reproduced light components undergo wavefront transformation to be separated at intervals of λf/P in each order of the diffracted waves on the rear focal plane of a lens provided behind the spatial light modulator. Here λ is the wavelength of the illumination light component, f the focal length of the lens, and P the pixel pitch of the spatial light modulator. Therefore, a desired 3D image is obtained in a manner of disposing a mask with an aperture of rectangular shape having the length of λf/P on each side on the rear focal plane of the lens and letting the zero-order diffracted wave of the reproduced light components pass through this aperture. The higher-order diffracted waves are blocked by this mask on the other hand.
In the above third conventional technology, concerning two adjacent pixels in the spatial light modulator, where the presentation range is limited to a range in which phase differences between synthetic wavefronts of an object light component and a reference light component are not less than π and are less than 2π (i.e., a range including a first-order alias component) and where a hologram is presented on the spatial light modulator, the wavefronts of the higher-order diffracted waves of the reproduced light components generated from the spatial light modulator upon incidence of the illumination light component coincide with the zero-order diffracted wave. For this reason, the zero-order diffracted wave and all the higher-order diffracted waves include their first-order alias component. Only a desired first-order diffracted wave among the reproduced light components can be extracted in a manner of disposing a mask with an aperture of rectangular shape having the length of λf/P on each side on the rear focal plane of the lens disposed behind the spatial light modulator and letting the first-order diffracted wave of the reproduced light components pass through this aperture. The zero-order diffracted wave and the second and higher-order diffracted waves are blocked by the mask on the other hand.
Namely, the above third conventional technology is to present the hologram on the spatial light modulator while limiting the presentation range to the range including the alias component of a specific order and to extract the diffracted wave of the specific order out of the reproduced light components by use of the mask with the aperture at the position corresponding to the specific order. The presentation of the hologram and the selection of the aperture associated with each order are implemented based on time-sharing or spatial synthesis, thereby enabling expansion of the emergence direction range of the reproduced image (i.e., a viewing area) formed by the lens.